import socket
import struct


def checksum(data):
    s = 0
    n = len(data) % 2
    for i in range(0, len(data) - n, 2):
        s += ord(data[i]) + (ord(data[i + 1]) << 8)
    if n:
        s += ord(data[i + 1])
    while (s >> 16):
        s = (s & 0xFFFF) + (s >> 16)
    s = ~s & 0xffff
    return s


class ip():

    def __init__(self, source, destination):
        self.version = 4
        self.ihl = 5  # Internet Header Length
        self.tos = 0  # Type of Service
        self.tl = 0  # total length will be filled by kernel
        self.id = 54321
        self.flags = 0  # More fragments
        self.offset = 0
        self.ttl = 255
        self.protocol = socket.IPPROTO_TCP
        self.checksum = 0  # will be filled by kernel
        self.source = socket.inet_aton(source)
        self.destination = socket.inet_aton(destination)

    def pack(self):
        ver_ihl = (self.version << 4) + self.ihl
        flags_offset = (self.flags << 13) + self.offset
        ip_header = struct.pack("!BBHHHBBH4s4s",
                                ver_ihl,
                                self.tos,
                                self.tl,
                                self.id,
                                flags_offset,
                                self.ttl,
                                self.protocol,
                                self.checksum,
                                self.source,
                                self.destination)
        return ip_header


class tcp():

    def __init__(self, srcp, dstp):
        self.srcp = srcp
        self.dstp = dstp
        self.seqn = 0
        self.ackn = 0
        self.offset = 5  # Data offset: 5x4 = 20 bytes
        self.reserved = 0
        self.urg = 0
        self.ack = 0
        self.psh = 1
        self.rst = 0
        self.syn = 0
        self.fin = 0
        self.window = socket.htons(5840)
        self.checksum = 0
        self.urgp = 0
        self.payload = ""

    def pack(self, source, destination):
        data_offset = (self.offset << 4) + 0
        flags = self.fin + (self.syn << 1) + (self.rst << 2) + (self.psh << 3) + (self.ack << 4) + (self.urg << 5)
        tcp_header = struct.pack("!HHLLBBHHH",
                                 self.srcp,
                                 self.dstp,
                                 self.seqn,
                                 self.ackn,
                                 data_offset,
                                 flags,
                                 self.window,
                                 self.checksum,
                                 self.urgp)
        # pseudo header fields
        source_ip = source
        destination_ip = destination
        reserved = 0
        protocol = socket.IPPROTO_TCP
        total_length = len(tcp_header) + len(self.payload)
        # Pseudo header
        psh = struct.pack("!4s4sBBH",
                          source_ip,
                          destination_ip,
                          reserved,
                          protocol,
                          total_length)
        psh = psh + tcp_header + self.payload
        tcp_checksum = checksum(psh)
        tcp_header = struct.pack("!HHLLBBH",
                                 self.srcp,
                                 self.dstp,
                                 self.seqn,
                                 self.ackn,
                                 data_offset,
                                 flags,
                                 self.window)
        tcp_header += struct.pack("H", tcp_checksum) + struct.pack("!H", self.urgp)
        return tcp_header


def test(source, site, data):
    s = socket.socket(socket.AF_INET,
                      socket.SOCK_RAW,
                      socket.IPPROTO_RAW)
    src_host = source
    dest_host = socket.gethostbyname(site)
    # IP Header
    ipobj = ip(src_host, dest_host)
    iph = ipobj.pack()
    # TCP Header
    tcpobj = tcp(1234, 80)
    tcpobj.data_length = len(data)
    tcph = tcpobj.pack(ipobj.source, ipobj.destination)
    # Injection
    packet = iph + tcph + data
    s.sendto(packet, (dest_host, 80))
    s.close()


if __name__ == '__main__':
    test("localhost", "www.baidu.com", "ITS TEST")
